addPolygon method
Adds a new subpath with a sequence of line segments that connect the given points.
If close
is true, a final line segment will be added that connects the
last point to the first point.
The points
argument is interpreted as offsets from the origin.
Implementation
void addPolygon(List<Offset> points, bool close) {
assert(points != null);
_addPolygon(_encodePointList(points), close);
}